Vehicles such as automobiles generally are provided with seat belt devices for restraining an occupant in a seat that includes a seat portion on which the occupant sits and a backrest portion positioned back of the occupant. Such a seat belt device includes a webbing for restraining the occupant, a retractor for retracting the webbing, a guide anchor that is disposed on a vehicle body side and guides the webbing, a belt anchor for fixing the webbing to the vehicle body side, a buckle disposed on a side surface of the seat, and a tongue disposed in the webbing. The tongue is fitted into the buckle to restrain the occupant in the seat with the webbing. In such the seat belt device, a first end of the webbing is fixed to the belt anchor, and a second end of the webbing is inserted into the guide anchor to be connected to the retractor.
It is becoming common that such the retractor has a pretensioner that eliminates slack in the webbing in an emergency such as a vehicle collision (e.g., refer to Japanese Translation of PCT International Application Publication No. 2007-522030). A pretensioner described in JP-T No. 2007-522030 includes a pinion gear coupled to a spool for winding a webbing, a power transmission member (load transmission element) for rotating the pinion gear in a vehicle collision, and a tube (pipe) that contains the power transmission member. Additionally, the power transmission member described in JP-T No. 2007-522030 is a plurality of mass bodies (balls).